This invention relates to the field of polymer blends, or alloys, and more particularly, to hydrophilic blends of polyurethane and poly(N-vinyl lactam) and to the use of these blends in a variety of applications including the formulation of lubricious coating compositions.
There has long been a need in the art for lubricious materials which are non-slippery when dry but exhibit lubricious or slippery properties when contacted with aqueous fluids. Applications for such materials are numerous and diverse and include fabrication into surface coatings, foams, fibers, films, or solid articles which absorb water, impart wettability or reduce the coefficient of friction in aqueous environments. Uses include, but are not limited to, coatings for catheters, condoms, invasive devices and test probes which are lubricious only when wet, antifog coatings for lenses, windows, etc., drag reducing coatings for ships, burn and wound dressings, contact lenses, antistatic coatings, hydrophilic fibers and matrices for controlled release of pharmaceuticals, dyes, fragrances, salts and the like. It had previously been proposed to reduce the coefficients of friction of these and similar devices and materials by the use of non-permanent coatings of silicone or certain fluorocarbons, neither of which are hydrophilic, and which do not have as low coefficients of friction as are necessary or desirable for some applications. The fluorocarbon coatings also have the disadvantage of being difficult to handle because they are always slippery, not just when slipperiness is desired.
Coatings and articles useful for insertion into the body, for example, are described in U.S. Pat. Nos. 4,100,309 and 4,119,094. Articles such as catheters and condoms described in these patents are obtained by coating a suitable substrate with a polyvinylpyrrolidonepolyurethane interpolymer. The coatings are obtained by a two-step procedure using first a solution of isocyanate containing prepolymer and polyurethane followed by a solution of polyvinylpyrollidone. The isocyanate can be modified with chain extenders (diols, etc.) which effectively produce a linear thermoplastic polyurethane in situ. This preparative route yields coatings which are not of uniform composition throughout (two separate layers intermixed at the interface) and are not suitable for the preparation of integral articles, films, foams or matrices with regular and uniform physical and mechanical properties. In addition, the requirement that reactive isocyanates be present introduces unavoidable chemical instability (pot life) and eliminates the possibility of utilizing aqueous or alcoholic solvents for preparation. Isocyanates will also react with and inactivate many desirable additives such as pharmaceuticals, surfactants and dyes.
U.S. Pat. Nos. 4,373,009 and 4,472,467 describe similar composition which can in some cases be applied from a single solution. These patents, however, require a chemical reaction forming a covalent bond between isocyanates and active hydrogen groups reactive toward isocyanates on the vinyl lactam or ethylene oxide polymers to produce the objects of the invention. These patents actually teach away from the use of chemically inert components.
Other lubricious hydrophilic coatings for a variety of uses are described in the prior art. For example, the practice of forming a linear polyurethane polymer and then dispersing it in water is well known in the art as shown in U.S. Pat. Nos. 3,412,054 and 4,094,838 which describe the preparation of modified, water dispersible urethanes.
Polyvinylpyrrolidone, a commercially available poly(N-vinyl)lactam, is a well known hydrophilic, polymer having numerous applications including being a film former, protective colloid and suspending agent, dye-receptive resin, binder and stabilizer, physiologically acceptable polymer, etc. However, being water soluble, polyvinyl-pyrrolidone and related poly(N-vinyl)lactams will eventually be leached from coating compositions and other materials formulated with the polymer when contacted with aqueous fluids. Thus, the practical value of known compositions containing polyvinylpyrrolidone as lubricious coatings is greatly limited due to the erosion of their lubricious properties as the polyvinylpyrrolidone component dissolves or is leached into the surrounding aqueous medium. Technical Bulletin 7583-033 of General Aniline & Film Corporation describes a variety of films containing a solvent-blended mixture of polyvinylpyrrolidone and another polymer, i.e., vinylchloride-vinylacetate copolymer, polyethylene, polyacrylonitrile, vinylidene chloride polymer, polyvinylisobutyl ether, polyvinylethyl ether, polystyrene, polyvinylchloride and polyvinyl alcohol. No suggestion is made in the technical bulletin of a blend of polyvinylpyrrolidone and a polyurethane.